Cutting blades which are used for slicing bread consist of a thin cross section blade in the form of a band. The band is of steel composition and has a cutting edge formed on the band, generally in the form of scallops, and a profile or contoured cutting edge in which the sides of the blade are inclined and terminate at the cutting edge of the scallops. The requirement for the cutting blade is that it have durability which makes for a long wear life of the blade, and also have the further capacity of making a clean slice through the bread or other material being cut. These characteristics are difficult to attain. For example, a profile which is effective for making a clean slice is frequently incapable of retaining its cutting edge over a period of time and requires frequent honing; because of the material removal, it is then impossible to secure a reasonable wear life for the blade. In broadest terms, the requirement for a good blade is that it function efficiently and cleanly in its slicing action and at the same time be sufficiently durable so that it will not have to be discarded after a relatively short period of use.
It is known that the profile of the blade, i.e., its cross sectional configuration, has an effect on slicing value or slicing efficiency. At the same time, if the profile should contain structurally weak areas, then rapid dulling, and subsequent resharpening, results in accelerated material removal by so-called "honing" operations with the result that the blade has to be soon replaced. Many proposals have been made, some of which have answered the one problem of cleaner slicing action, others of which have answered the other problem of meeting the need of greater wear life. But the art has failed to produce a cutting blade to meet the requirements for clean slicing of bread and at the same time to achieve a material factor of improvement in the wear life.
What is the foremost object of the present invention is to produce a new profile of blade in which integrally related to the thin, flexible base, is a reduced cross section shank having shoulders at the intersection, or juncture, between the shank and the base. At the end of the shank is a continuously formed scallop which forms the cutting edge with the scallop cutting edge being formed from the opposite sides which taper toward each other and intersect at the cutting edge.
It is thought that the reason for the improved combination of greater wear life and cleanness of slice provided by this novel blade configuration is the relief which is provided between the cutting edge and the base. Thus, as the cutting edge passes into the bread it is followed not by a relatively thicker cross section base, but by a relatively thin cross section shank which tends to hold the cutting edge against bending out of the cutting plane, and precluding tearing, as distinguished from clean slicing, and adding to the friction which can contribute to the wear rate. Therefore, it can be seen from the blade configuration itself that what might very well account for this combination of improvements is the manner in which the blade is successively stepped first from the cutting edge then through the inclined honed section of the cutting edge to the narrow cross section shank and then to the larger cross section base.
While these are advanced as possible reasons accounting for the improved results, the explanation is theoretical, and, whether correct or not, the structure itself is inherently an improvement in combining the features of greater wear life and cleaner slicing action.
Another object of the present invention is to employ a new process and apparatus, which entails new grinding techniques for material removal in a continuous manner and without encountering such high degrees of heat and abrasion as will in any way temper or moderate the strength of the steel composition of the blade. To accomplish this, there are utilized two grinding wheels which employ flat annular grinding surfaces, one wheel bearing against one side of the blade and the other wheel bearing against the opposite side of the blade to produce the material reduction and form the intermediate shank of narrow cross section. Generally, this step is performed after the scalloping-and-edge cutting is performed on the blade so that the blade is passed continuously between the two grinding wheels where the final material removal is effected, which configures the shank. The grinding wheels are comprised of cubic boron nitride of special composition known as "Borazon CBM" (a trademark for material obtained from General Electric and formed into a borazon wheel by the Norton Company, Form 3509 2P-PXM-4-74).
In the present invention, it is an important object to provide an apparatus and process by which the cutting blade passes continuously between slideable gripping means which hold the blade at its correct position in relation to these grinding wheels with a two-stage grinding wherein grinding occurs first on one side and then the opposite side of the blade to produce the final configuration.
Another object of the present invention is to employ a new and novel apparatus which is adaptable for different hoop length blades and capable of retaining such blades under preferred tension effecting their continuous, or endless, rotation so that as the blades rotate they are both ground and yieldably gripped so as to be positioned at a preferred angle during the grinding operation. The result is a particular profiled blade having a requisite depth, cross section, inclined sides, and cutting edge ideal for a given cutting operation.
A further object of the present invention is to provide an apparatus which can be both manually controlled and timer controlled so that either a predetermined period of grinding action can be imposed on the machine and at the end of such machine operation the blade will be completely ground and the given profile edge formed thereon, or the operation can be extended or cut short.
Another object of the present invention is to provide a grinding apparatus and process which is capable of employing the relatively new but as yet nonextensively used cubic boron nitride composition grinding wheel which acts as a superabrasive. In spite of the greater expense of this material, it is capable, when employed in the present process and apparatus, of producing a grinding action on a blade and producing the blade with an acceptable wear life such that blades can be produced at a competitive cost even though the grinding wheels are very expensive.
An important feature of the present invention is that during the grinding operation the positioning of the blade and retention of the blade are precisely obtainable in relation to the grinding wheel so that an exact profile for the cutting edge is obtainable notwithstanding slight variations in dimension of the width of the blade. Thus, the blade is mountable on the apparatus, the grinding operation can be commenced, and will continue for a prescribed period of time at the end of which the blade is fully ground and the exact profile is imposed on the blade, this in spite of the fact that there are inevitably various dimensional variations in the thickness of the blade. Moreover, the apparatus is equipped with manual override means so that the grinding operation can be either intermittent, discontinued, stopped and recommenced in the middle of a grinding cycle. The blades are easily installed, tensioned, ground, and then replaced with the aid of power means in order to obtain the greatest blade production.
Adjustments in positioning of the grinding wheel and blade during grinding are all contemplated to be, and in fact are, relatively easy adjustments, and they are micrometric to obtain a fine degree of variation in blade profile to achieve the exact results.
Other objects and features of the present invention will become apparent from a consideration of the following description, which proceeds with reference to the accompanying drawings wherein certain selected example embodiments of the invention are illustrated by way of example and not by way of limitation.